PHP与MS SQL Server无法正常工作

Question

This my first time to create php form. I want to submit the form data to ms sql server database in my web server. I am using IIS ver 7.5.7600.16385 and ms sql server 2014 express edition and ms sql server management studio 2017. I m not able to connect to my sql server using the simple below file:

I checked all the configuration required in terms of dll in EXT folder , but not working.the follwoing are dll files :

- php_pdo_sqlsrv_53_ts.dll
- php_pdo_sqlsrv_53_nts.dll
- my php vesrion is 5.6.31

This is my file php code:

<?php 
 $mssqldriver = '{SQL Server}'; 
 $mssqldriver = '{SQL Server Native Client 11.0}'; 
 $mssqldriver = '{ODBC Driver 11 for SQL Server}'; 
 $hostname='127.0.0.1'; $dbname='BGEnqiry'; $username='sa'; 
 $password='123321'; 
 $conn=newPDO("odbc:Driver=$mssqldriver;Server=$hostname;Database=$dbname", $username, $password); 

if( $conn ) { 
 echo "Connection established.<br />"; 
}
else{ 
 echo "Connection could not be established.<br />"; 
 die( print_r( sqlsrv_errors(), true)); } ?>